Synthetic polymeric filaments are relatively weak as they are extruded from a spinneret. Therefore, they are drawn to several times their initial length during the subsequent transport via rolls so as to orient their molecules in the lengthwise direction. The drawing is performed between two feeder rolls driven at different feeding speeds between which rolls a draw pin is arranged along the circumferential surface of which the filaments are frictionally moved at a wrap angle. The draw pin concentrates the drawing effect at a specific point on the filaments' path, namely the point immediately behind the draw pin.
Draw pins are subject to high wear. The friction of the filaments on the pin causes grooves in the surface of the draw pin. This is particularly a problem with filaments containing pigments where, especially at higher drawing speeds, the very fine and hard pigment particles cut into the surface of the draw pins. With a worn down surface of the draw pin, the draw pin generates increased friction, there being the danger of filament damage or even of filament rupture. Therefore, it is necessary to regularly change the portion of the draw pin surface that is in contact with the filaments Customarily, the draw pins that are fixedly mounted on the drawing device in a defined position are loosened and rearranged so that another surface portion is used. To do so, however, the machine must normally be stopped. If it is not stopped, there is considerable risk of injury to the machine operator's fingers since the rearranging procedure requires operations in the immediate vicinity of the running filaments. Upon changing the portion contacted by the filaments, a "sawtooth effect" will occur. This means that the filaments first run over a not worn down area of the draw pin, which area will become increasingly worn down during further operation, and that eventually the quality of the filaments will deteriorate. If the draw pin is subsequently placed elsewhere, the filaments will first pass over a not worn down area which again will deteriorate increasingly. Thus filament quality varying in time is obtained
U.S. Pat. No. 3,776,796 and German Patent 37 05 105 describe drawing devices wherein the draw pin is continuously rotated by a slowly running drive in order to change the active portion of its surface. Such a slowly running rotating drive requires considerable effort since it requires a motor and, usually, a stepdown gear. Moreover, there is constant consumption of energy.
It is the object of this invention to provide a drawing device for synthetic filaments that, without requiring a drive means, allows a change of the contact portion of the draw pin while filament transport continues, and that also ensures uniform filament quality.